Skeleton and skull of WIGM SPC V 1107, holotype of “Atopodentatus unicus” (Cheng et al., in press). Skull shown is the other side.

“Atopodentatus unicus” looks a lot like many other primitive marine reptiles, with a long narrow body and short, stubby legs, a sort of Dachshund of the sea. What you think you see, however, is an illusion crafted by your mind to hide the awful truth that this animal is not appropriately named (no insult to the authors; this whole post is meant somewhat in jest, as that is my only way to cope).

Discovered as a part of the Late Triassic Luoping fauna of Yunnan Province, China, it (described by Long Cheng and Xiao-hong Chen from the Wuhan Institute of Geology, Wuhan, China; Qing-hua Sheng from the Institute for Paleontology and Paleonanthropology, Beijing, China; and Xiao-chun Wu from the Canadian Museum of Nature, Ottawa, Canada) is one of the most bizarre marine reptiles known. It doesn’t look it, once you get past the squashed, short face. The long body is fairly sausage-like, with slender ribs, a gastral basket, and well-developed pelvic and pectoral girdles for supporting the limbs, fairly long humerus and femur. It has a relatively short neck compared to most non-placodont marine reptiles, and the small head in connection with a barrel shaped body recalls basal placodonts like Placodus gigas, which may have been herbivorous to some degree. It had hoof-like terminal phalanges, a feature of marine reptiles only known in the placodont Psephoderma alpinum (itself a strange animal), which combined with a pelvis firmly connected to well-developed sacral ribs suggests the limbs may have been well-suited to life on land. But that’s what you get when you’re not looking at the head. At this point, you’re thinking “pretty strange basal placodont-like fellow,” right?

Phylogeny of Cheng et al (in press) showing position of their new taxon between Sauropterygia and Saurosphargidae.

Cheng et al. performed a systematic analysis (adding to the work of Li et al., 2013 on Largocephalosaurus qianensis, a “saurosphargid” — another contentious group of near-sauropterygians) and found that “Atopodentatus unicus” groups right outside the clade that includes placodonts and sauropterygians proper, with saurosphargids the sister taxon this this group. These are all either long necked, sleek predatory animals, or else squat, bulky, more sedentary durophages or herbivores (really, reptilian manatees as some have compared placodonts, but see here and here). But aside from placodonts, this group seems to be just one iteration of predator after another.

Well — then you look at it’s face.

A Cartoon Reptile For Real

Photograph and line-drawing of skull in right view of WIGM SPC V 1107, holotype of “Atopodentatus unicus” (Cheng et al., in press).

At first glade it appears distorted. The face looks like what you get when a cartoon character runs full into a wall that some other character has painted to look like a tunnel. The nose squishes and turns down, and everything else just crumples. But look closer. The nostrils are pulled back from the snout, the mandible seems to be curved downward, and rather than crushed the bone surfaces seem to be smooth and intact (there’s a crack that runs through the skull, but this is not aligned to where the skull would be “crushed” inward, and is a post-preservation artifact).

“Atopodentatus unicus” has a lot of teeth and they are tiny, thin, and needle-like. They possess enamel, are closely packed, and look nothing more than a toothy version of whale baleen. We’ll get back to that in a bit (Cheng et al. suspect it was a suspension feeder due to the closely-packed teeth). The teeth seem to be arrayed on the mandible around the edge, but because of the downturn the teeth follow suit. Both sides of the jaw show the same thing, suggesting this shape is not a distortion. Cheng et al. suggest that the skull was originally quite broad in the snout originally, and that the mandible would have been rather scoop-like in shape.

Look closely at that maxilla. Look how L-shaped it is. Seems wonky, right? Here’s the other maxilla, broken off from the skull:

Left maxilla of WIGM SPC V 1107, holotype of “Atopodentatus unicus” (Cheng et al., in press) in medial view. Dorsal is to the top, anterior to the right.

That fluting on the inside are the dental grooves for teeth, which are implanted in pleurodont fashion: to the sides of the bones, not in socked or on the bone edge, with connective tissue at the base and along the groove. There are a lot of them, and they continue from the back end all the way to the tip of the other. The tip of the “flattened nose.” The other edge of the maxilla attaches the premaxilla, but as can be seen in the skull above, the premaxilla doesn’t extend any further down. But it also has teeth. And this is where your mind realizes that the name, “Atopodentatus unicus” (meaning “unique strangely toothed”) is likely not an appropriate name. Certainly, it captures some aspects of the animal well, but it doesn’t capture how irregular this taxon is. How … chthonic it is.

Indeed, a better name might have been “Chthulhudon” or “Schizorostra.” That last one is, I think, inspired, because if you turn the snout ever so slightly, you find that …

… the premaxillae are not connected on their medial margins, based on the absence of a thick symphyseal border, which instead bear all those “missing” premaxillary teeth. The grooves of the premaxilla are also wider than those of the maxilla, in case anyone is trying to think these are the same grooves for the maxillary teeth. Oh, no, those are for MEDIALLY POINTING TEETH that form a mesh between the tentacle-like split upper maw, looking so much like a pair of serrated tentacle feelers of some Mindflayer or chthonic horror from H. P. Lovecraft. And, appropriately, your mind just explodes thinking about this.

There’s just got to be a saner explanation for this snout, right? Right? Here we have what may just seem to be an animal capable or even adapted to hoofing it around on land on occassion, but when suitably impressed with its achievement of having survived a day out and about slips under the water and into the cold, murky abyss of the eastern edge of the shallow (but very abyssal, for what else could this animal enjoy?) Tethys to find planktonic or algal food and strain it through its fine teeth, splitting its hideous maw at any bypassing nothosaur or pistosaur and freaking them the hell out as they gaze deep, deep into the split where its nose really should be … and where naught but madness lies.

From Oclaf.

[n1] The name is currently published only online in a digital form; however, Naturwissenschaften notes that online publication of nomenclature is “valid” so far until the paper version comes out, which then becomes the correct citation date. This is a tricky grey area when it comes to the problems of “published ahead of print” names, as this proliferates names that aren’t “available” and treated as such. For reasons including my sanity, they grey area, and because conversation about this animal already occur, I have chosen to use the name as cited. When this page was first published a little over an hour before this note, I used the name without quotes and in italics, but am switching to the “scare quotes” (yeah, those) and removing italics until the citation below is published in paper.

17 Responses to I’m Not Sure That Name Is Appropriate

Wait, what? So, instead of a snout, this…. thing had a split over it’s actual mouth, with more teeth in it. Wow. If that skull wasn’t attached to a fairly reasonable skeleton, I’d doubt it’s native to this planet.

Is there evidence showing that the angle between the two premaxillae was actually as small as the reconstruction suggests? It would seem more functional if there was a greater angle between them such that the lower jaw could then pass between them, with the lower teeth combing through the upper teeth.

My thought is that the premaxillae are connected along their entire midline. But the margin that might be the symphysis of the premaxillae in the fossil is a thin edge, with no trace of an actual symphyseal joint. There are larg-ish teeth in the upper oral vault behind the intact (nondeflected) premaxilla, and they point backwards into the throat, and these are the only premaxilla-sized teeth in the fossil. I’m wondering (as are a few others) that these are rear-ward, not medial, premax teeth. But this doesn’t tell me what the premaxillae are really doing.

It looks kind of like an anomalocaridid. Two paired, downward-facing appendages (premaxillae/maxillae versus “great appendages”, combined with a pair of medially facing spines/teeth to keep prey from escaping.

This has a horizontal “normal” mouth. It just also has a harelip. While the gug reference is fitting (the vertical mouth is definitely worth the squick, as in the aliens from The Last Starfighter, or Turanga Morris, Leela’s father) for the harelip, the comparison stops there. I am not so familiar with the mythos that I knew what gugs were before I posted this, or I’d have made some aside on specific horrors. The face LOOKs at first like there’s a mouth with tentacular overhangs, and so I went with the most well-known from the mythos. Apologies to all Lovecraftians out there.

What scares me more is what the beast used that horrible diastema for. I see parallels between its jaws and those of flamingos, and they were probably used the same way: to filter shrimps and other small arthropods from water and then expel the water. The difference, of course, is that the water pistoned out of a flamingo’s jaw by its tongue goes out laterally and not straight out the front. I keep getting the image of Atopodentatus actively spitting water out of that diastema, either for display or as a possible defense. In that case, “Gleekosaurus” would probably be a lot more accurate.

I’m curious about how these structures evolved. It wasn’t enough to split the rostrum, but develop two distinct rows of teeth in the middle of the gap. My best guess is that, rather than splitting the rostrum, this biforcation evolved from “bumps” on the premaxilla.